Differential pulse amperometric detection

Hikima S., Kakizaki T., Hasebel K., Enzyme sensor for L-lactate using differential pulse amperometric detection, Fresen. J. Anal. Chem. 1995 351(2-3) 237-240. 

M.R. Hackman and M.A. Brooks, Differential pulse amperometric detection of drugs in plasma using a dropping mercury electrode as a high-performance liquid chromatographic detector, J. Chromatogr., 1981, 222, 179-190. 

F. Elferink, W.J.F. van der Vijgh and H.M. Pinedo, Analysis of antitumour [1,1-bis(aminomethyl)cyclohexane]platinum(II) complexes derived from spiroplatin by high-performance liquid chromatography with differential pulse amperometric detection, J. Chromatogr., 1985, 320, 379-392. 

W.J.F. van der Vijgh, H.B.J. van der Lee, G.J. Postma and H.M. Pinedo, Highly sensitive differential pulse amperometric detection of second-generation antitumour platinum compounds in h.p.l.c. eluents, Chromatographia, 1983, 17, 333-336. 

D. G. Swartzfager, Amperometric and differential pulse voltanunetric detection in high performance liquid chromatography, Anal Chem., 48,2189,1976. 

SCX column was used to separate oxalate and urate.140 In this separation, differential pulse and DC amperometric detection were compared. Differential pulse detection was found to allow better selectivity in detection. Anion exchange on Diaion CA08 was used to separate 20 carboxylic acids in the analysis of white wine, as shown in Figure 10.141 Because many carboxylic acids have a relatively weak absorbance, detection is difficult. The colorimetric detection scheme shown in the figure may be useful in some applications. 

Mayer, W. J. and Greenberg, M. S., A comparison of differential pulse and D. C. amperometric detection modes for the liquid chromatographic determination of oxalic acid, /. Chromatogr Sci., 17, 614, 1979. 

Electrochemical biosensors have some advantages over other analytical transducing systems, such as the possibility to operate in turbid media, comparable instrumental sensitivity, and possibility of miniaturization. As a consequence of miniaturization, small sample volume can be required. Modern electroanalytical techniques (i.e., square wave voltammetry, chronopotentiometry, chronoamperometry, differential pulse voltammetry) have very low detection limit (1(T7-10 9 M). In-situ or on-line measurements are both allowed. Furthermore, the equipments required for electrochemical analysis are simple and cheap when compared with most other analytical techniques (2). Basically electrochemical biosensor can be based on amperometric and potentiometric transducers, even if some examples of conductimetric as well as impedimetric biosensor are reported in literature (3-5). 

The equipment widely used for the detection of carbohydrates in the HPLC method is the differential refractive index (RI) detector. The principle involved in this detection depends on the continuous measurement of the variation of the RIs of the mobile phase containing the samples with little or no chromophores such as carbohydrates, lipids, and other polymer compounds that do not absorb UV light. RI detection method presents high degree of reproducibility and is very convenient for the analysis of polysaccharides. However, other detectors such as evaporative light scattering detector and pulsed amperometric detector have been used for the detection of polysaccharides [100]. 

Voltammetric techniques that can be applied in the stripping step are staircase, pulse, differential pulse, and square-wave voltammetry. Each of them has been described in detail in previous chapters. Their common characteristic is a bell-shaped form of the response caused by the definite amount of accumulated substance. Staircase voltammetry is provided by computer-controlled instruments as a substitution for the classical linear scan voltammetry [102]. Normal pulse stripping voltammetry is sometimes called reverse pulse voltammetry. Its favorable property is the re-plating of the electroactive substance in between the pulses [103]. Differential pulse voltammetry has the most rigorously discriminating capacitive current, whereas square-wave voltammetry is the fastest stripping technique. All four techniques are insensitive to fast and reversible surface reactions in which both the reactant and product are immobilized on the electrode surface [104,105]. In all techniques mentioned above, the maximum response, or the peak current, depends linearly on the surface, or volume, concentration of the accumulated substance. The factor of this linear proportionality is the amperometric constant of the voltammetric technique. It determines the sensitivity of the method. The lowest detectable concentration of the analyte depends on the smallest peak current that can be reliably measured and on the efficacy of accumulation. For instance, in linear scan voltammetry of the reversible surface reaction i ads + ne Pads, the peak current is [52]... 

Conductivity, direct absorbance or a differential refractometer are the most common forms of detection for lEC, PAD and ELSD. A pulsed amperometric detector (PAD) or, more recently, an evaporative light-scattering detector (ELSD) is appropriate for detection of carbohydrates. Both non-suppressed and suppressed conductivity have been used extensively. The need to incorporate a low concentration of a strong acid into the eluent has been an impediment to direct conductivity detection. 

Inczeffy, J., Somodi, Z.B., Pap-Sziklay, Z. and Farsang, G. (1993) The study of the differential pulse voltametric behaviour of ergot alkaloids and their determination by DC amperometric detection in a FIA system./. Pharm. Biomed. Anal, 11,191-196. 

The most elementary biosensors are fruit pulps or slices which have been combined with amperometric electrodes. A well-known example is the ba-nanatrode (Wang and tin 1988). This sensor, most useful for demonstration experiments, contains a paste mix of banana pulp, nujol and carbon powder which has been pressed into a glass tube with an electric contact (Fig. 7.39). The mass contains the enzyme polyphenolase, which catalyses the oxidation of polyphenols, among them important biological messengers like dopamine. The sensor can be tested by means of simple compounds like catechol, which can be detected in beer. As a result of air oxidation, o-quinone is formed. The latter is an electrochemicaUy active compound which can be detected e.g. by differential-pulse voltammetry. 

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